As a contactless automatic identification technology, Radio Frequency Identification (RFID), having a data transmission function with low power consumption, may be applied to logistics management, identity recognition, transportation, food and healthcare, animal management and many other fields. RFID tag systems are mainly divided into two types: passive RFID tags, i.e., RFID tags not to be powered by a power supply; and active RFID tags, i.e., RFID tags to be powered by a power supply. When a passive RFID tag operates, the energy required for its operating circuit is converted from the energy of an electromagnetic field. Due to their low cost, high level of integration, flexible packaging, long service life and the like, passive tag systems are particularly suitable for warehouse management, food and healthcare, animal management or other fields.
Temperature sensors have been widely applied to the fields of industrial control, healthcare and measurement. In an integrated electronic system, the temperature sensors generally exist in two forms:
One form is that temperature sensors are independent from an integrated circuit, that is, there are temperature sensor chips independent from the integrated electronic system. For example, the integrated electronic system measures temperature by an external thermistor. In an integrated electronic system, such individual temperature sensor chips have the characteristics of high cost, large packaging volume and the like. As a result, the application fields of such temperature sensors are limited. For example, such temperature sensors are unable to perform temperature measurement well in warehouse management, food and healthcare, animal management or other fields.
The other form is that a chip having a temperature measurement function is built-in an integrated electronic system. At present, the temperature measurement technology with built-in chips has been widely applied to integrated electronic systems. For this technology, in the case that there is a power supply available, a physical quantity (e.g., current) in direct proportion to the absolute temperature is obtained in such a way that a bandgap reference voltage is generated by acquiring a difference in voltage between PN junctions of a semiconductor chip. If a chip having a temperature measurement function is built-in a passive RFID tag, a passive RFID tag having the temperature measurement function may be obtained. After the temperature collection and measurement is performed by using the passive RFID tag, a physical quantity indicative of temperature is obtained. As the physical quantity is usually an analog signal, the passive RFID tag usually performs analog-to-digital conversion on the physical quantity, i.e., converts the physical quantity into a digital code in certain accuracy. For example, the passive RFID tag converts an analog quantity indicative of a change in temperature of 1° C. into a 10-bit binary digital code, where the change in temperature indicated by each bit of digital code is less than 0.001° C.
Specifically, during temperature measurement, a passive RFID tag needs to absorb energy from a surrounding electromagnetic field first, where the energy is specifically embodied in AC on an inductive coil; and then, the passive RFID tag converts the absorbed energy, i.e., from AC to DC, by an analog front-end receiving circuit, so as to obtain a DC power supply voltage for the operation of the whole passive RFID tag. During the temperature measurement performed by using a passive RFID tag, on one hand, as each module of the passive RFID tag is limited in restraining the AC disturbance to the power supply voltage, the node voltage of each module will be modulated by the disturbed power supply voltage to varying degrees, and such modulation disturbance, in the nature of noise, will impede the accuracy of temperature measurement performed by using the passive RFID tag; and on the other hand, during the manufacturing of a passive RFID tag by a semiconductor chip manufacturer, as the manufactured RFID tag is subjected to the processes, the performance of the circuits will be fluctuated to varying degrees. Such fluctuation directly results in a large range of errors and inconsistency, in converting a physical quantity indicative of temperature, of different RFID tags manufactured by a same semiconductor chip manufacturing process. In other words, it is likely to obtain different digital codes when a same temperature is measured by using different RFID tags. That is, different values of temperature will be obtained when a same temperature is measured by using different RFID tags. Thus, it is unable to ensure the consistency of temperature measurement of passive RFID tags. For batch products, this is a fatal weakness which directly affects whether or not the products may be introduced to the market and accepted by users eventually.